The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to a method of fabricating and using an image sensor package.
Image sensors and assemblies are well known to those of skill in the art. In these assemblies, an image sensor was located within a housing which supported a window. Radiation passed through the window and struck the image sensor which responded to the radiation.
Beaman et al., U.S. Pat. No. 5,821,532, which is herein incorporated by reference in its entirety, teaches an image sensor assembly. In the assembly, an image sensor was mounted to a printed circuit board. After the image sensor was mounted, a housing was mounted around the image sensor and to the print circuit board. This housing provided a hermetic like barrier around the image sensor, while at the same time, supported a window above the image sensor.
As the art moves to smaller and lighter weight electronic devices, it becomes increasingly important that the size of the image sensor assembly used within these electronic devices is small. Disadvantageously, conventional image sensor assemblies required a housing to support the window and to hermetically seal the image sensor. However, these housings are relatively bulky and extend upwards from the printed circuit board a significant distance, e.g., 0.100 inches (2.54 mm) to 0.120 inches (3.05 mm) or more.
In addition, mounting these housings at the printed circuit board level was inherently labor intensive and made repair or replacement of the image sensor difficult. In particular, removal of the housing exposed the image sensor to the ambient environment. Since the image sensor was sensitive to dust as well as other environmental factors, it was important to make repairs or replacement of the image sensor in a controlled environment such as a cleanroom. Otherwise, there was a risk of damaging or destroying the image sensor. Since neither of these alternatives are desirable and both are expensive, the art needs an image sensor assembly which is simple to manufacture and service so that costs associated with the image sensor assembly are minimized. Further, the image sensor assembly should be relatively thin.
In accordance with the present invention, an image sensor package includes an image sensor having an active area which is responsive to radiation. The image sensor is mounted to a substrate which is transparent to the radiation. The image sensor is mounted such that the active area of the image sensor faces the substrate.
During use, radiation is directed at the substrate. This radiation passes through the substrate and strikes the active area of the image sensor. The image sensor responds to the radiation in a conventional manner.
Of importance, the substrate serves a dual function. In particular, the substrate is the window which covers the active area of the image sensor. Further, the substrate is the platform upon which the image sensor package is fabricated.
Recall that in the prior art, a housing was used to support the window above the image sensor. These housings were typically formed of ceramic which is relatively expensive. Advantageously, an image sensor package in accordance with the present invention eliminates the need for a housing of the prior art. Accordingly, the image sensor package is significantly less expensive to manufacture than image sensor assemblies of the prior art.
In one embodiment, a bead is formed around a periphery of the image sensor such that the image sensor, the bead, and the substrate form a sealed cavity. The active area of the image sensor is located and hermetically sealed within this cavity. Hermetically sealing the active area reduces complexity and cost in the event the image sensor must be repaired or replaced compared to the prior art.
Recall that in the prior art, the housing which hermetically sealed the image sensor was mounted directly to the larger substrate. Thus, removal of the housing necessarily exposed the image sensor to the ambient environment and to dust. For this reason, the image sensor had to be repaired or replaced in a cleanroom or else there was a risk of damaging or destroying the image sensor.
In contrast, the active area is hermetically sealed as part of the image sensor package. The image sensor package is mounted to the larger substrate. To repair or replace the image sensor, the image sensor package is simply removed and a new image sensor package is mounted to the larger substrate. At no time is the active area exposed to the ambient environment during this procedure. Advantageously, this procedure can be performed in any facility with or without a cleanroom. The old image sensor package is discarded or shipped to a central facility for repair. Since the image sensor package is simple to manufacture and service, the cost associated with the image sensor package are minimized compared to the prior art.
Further, the image sensor package is relatively thin compared to prior art image sensor assemblies. In particular, by mounting the image sensor directly to the substrate which also serves as the window for the image sensor, the resulting thickness of the image sensor package is relatively small, e.g. is 0.99 millimeters (mm). Recall that in the prior art, the image sensor was mounted directly to the larger substrate and a housing was used to support a window above the image sensor. This housing extended a significant distance, e.g., 0.100 inches (2.54 mm) to 0.120 inches (3.05 mm) or more, from the larger substrate. Since the image sensor package in accordance with the present invention is relatively thin compared to an image sensor assembly of the prior art, the image sensor package is well suited for use with miniature lightweight electronic devices which require thin and lightweight image sensor assemblies.
In another embodiment, a step up ring is used to elevate interconnection balls above the image sensor, the interconnection balls being used to connect the image sensor package to a larger substrate such as a printed circuit mother board. Advantageously, use of the step up ring allows the interconnection balls to have minimum size and pitch. This may be important, for example, when a large number of interconnection balls must be provided in a limited area.
In one embodiment, a plurality of image sensor packages are fabricated simultaneously to minimize the cost associated with each individual image sensor package. In accordance with this embodiment, image sensors are attached to an array type substrate which includes a plurality of individual substrates integrally connected together. Beads are formed around the peripheries of the image sensors. The array type substrate is then singulated, either before or after the array type substrate is populated with interconnection balls or other interconnection structures.
By forming a plurality of image sensor packages simultaneously, several advantages are realized. One advantage is that it is less labor intensive to handle and process a plurality of image sensor packages simultaneously rather than to handle and process each image sensor package on an individual basis. By reducing labor, the cost associated with each package is minimized.
In one embodiment, an image sensor package includes an image sensor having a bond pad and an active area responsive to radiation. The image sensor package further includes a substrate transparent to the radiation and an electrically conductive trace formed on the substrate. The bond pad is electrically connected to the trace.
In another embodiment, a method of using an image sensor package includes forming a trace on a substrate, attaching a bond pad of an image sensor to the trace, and directing radiation at the substrate. The radiation passes through the substrate and strikes an active area of the image sensor.
In yet another embodiment, a method of forming an image sensor package includes forming a trace on a substrate. A bond pad of an image sensor is attached to the trace. A bead is formed around a periphery of the image sensor. The image sensor, the bead, and the substrate defined a cavity. An active area of the image sensor is located within the cavity.
These and other features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.